Climate change can seem almost too big to fathom. Reports such as the recent National Climate Assessment and the United Nations Intergovernmental Panel on Climate Change’s recent release have made waves by portraying the dire threats of a warming world, making the case that the fundamental fabric of humanity will be degraded without immediate action. But the scenarios—the biblical floods and droughts, the mass migrations of dispossessed people, the creeping seas and the retreating glaciers—have a way of short-circuiting the brain. It’s almost easier to despair or to will oneself into ignorance than to begin to grapple with the future. What are human lives when measured against the coming tempest?

Efforts to assess the exact human costs of climate change, however, have provided new tools for understanding the ways in which those lives will be impacted. A major report published November 28 in the public-health journal The Lancet provides predictions of how climate change is degrading human health, and how it will alter health-care systems in the future. The findings are reliably grim. But in focusing on the health-care implications and the potential damage done to people and their descendants, the report provides a firm backing to the call to climate action. The experts behind the report hope to marry the urgency of climate science with the muscle of America’s most successful and most trusted policy experiment—its public-health system.

The report, sponsored by 27 academic institutions, a collection of intergovernmental agencies, and the UN, features an American Public Health Association–sponsored supplement dedicated to the specific effects of climate change on America. The authors Renee Salas, Paige Knappenberger, and Jeremy Hess examine what they propose are the three main ways in which a warming world will affect the health of Americans. For one, the heat itself and the increased intensity and duration of heat waves will make people sick, along with exacerbating existing conditions and reducing the productivity of workers. Second, as has been demonstrated in recent disasters, the rising severity and frequency of extreme weather events will elevate threats to health, as well as threats to health systems. Third, warmer seasons and warmer water mean the range for illnesses carried by ticks and mosquitoes will expand, putting more Americans in the crosshairs of diseases such as vibrio, Lyme disease, and West Nile.

The actual “warming” of global warming is an issue that is often curiously overlooked in terms of its direct effects on human lives. But as The Lancet’s report shows, it’s the most predictable component of a changing climate, and also the one with measurable effects already. The report points to evidence already indicating links between hotter temperatures and mental-health and cognitive issues; increases in kidney diseases, preterm births, and respiratory diseases; heat exhaustion; and the advance of antibiotic-resistant bacteria. One estimate cited in the report finds that more than 3,000 additional people across the country will die prematurely because of higher temperatures by 2050.

Released just days after the catastrophic fires that burned Paradise, California, were contained, The Lancet’s paper also studies the effects of extreme weather events on health. “Since 1980, there has been a steady rise in billion-dollar weather and climate disaster in the U.S.,” the authors write, citing data from the National Oceanic and Atmospheric Administration. But that finding doesn’t quite capture how much more common extreme events have become, or how much their magnitude has increased in a short time. In 1984, there were two weather events that exceeded $1 billion of damage in today’s dollars, with a five-year average of about $40 billion a year in costs from extreme events. In 2017, there were 16 such events, with a five-year average north of $200 billion in annual costs. With each of those events comes both direct risks to human lives and indirect risks associated with the collapse of health-care services and the spread of infectious diseases—consequences that were already highlighted in the deaths of thousands of people in the aftermath of Hurricane Maria in Puerto Rico in 2017.

“Perhaps one of the most startling facts is that we truly have climate refugees within the United States,” Salas said in a conference call before the brief’s release. “I think that this is something that a lot of individuals within the U.S. think is a distant effect, but it’s truly something that we’re seeing here today. In fact, earlier this year I had a patient who came from Puerto Rico. She was elderly, she showed up with her luggage, and truly had a bag with medications that she hadn’t taken in a few weeks … She was truly a climate refugee.” And, as Salas notes, the most vulnerable populations to a whole range of health problems are those that have been recently displaced. As has emerged recently in studies of disaster-affected communities, they also suffer post-traumatic stress and a uniquely high mental-health burden that can persist for years.

It’s no wonder that displacement and the long-term effects of disasters are also wrapped up with spikes in diseases carried by mosquitoes, ticks, and fleas, and those transmitted by pathogens in warm water. In tropical Puerto Rico, Zika outbreaks before the storm led to fears of even greater outbreaks after the storm. But on the more temperate mainland, the real risk is the spread of subtropical diseases to places where temperatures were once too cold to support the diseases. The Lancet’s report cites another from the Centers for Disease Control and Prevention that shows that disease cases from mosquitoes, ticks, and fleas more than tripled from just under 30,000 to almost 100,000 a year from 2004 to 2016, and also highlights a steady increase in the viability of vibrio, a bacteria found in warm waters that can cause life-threatening infections of gastroenteritis.

According to Gina McCarthy, the director of the Center for Climate, Health, and the Global Environment and a former administrator of the Environmental Protection Agency under President Barack Obama, the increased geographic spread of these diseases can reverse the signature gains of the past century of American health policy—namely, the near-eradication of many of the communicable infectious fever diseases that have always haunted humanity. “You’re seeing challenges as broad as Massachusetts, where you’re seeing that West Nile virus is increasing,” she said on the conference call, “or Lyme disease, because of species of mosquito that are spreading diseases that we weren’t familiar with years ago, that are now becoming commonplace.”

In a forum by the American Public Health Association (APHA) and the Harvard Global Health Institute discussing The Lancet’s global report and its brief for the United States, the authors and several public-health experts stressed to me that these findings were only the tip of the iceberg of some truly unforeseen future effects, that they were only examples of larger global trends, and that they don’t reflect far-off future scenarios but rather what is currently observable in existing climate change.

“In recent years, we have understood the importance of heat and climate change on the impacts of farmworkers who are working outdoors in some of the most difficult conditions just so Americans can have food to eat,” said Jeannie Economos, the pesticide-safety and environmental-health project coordinator at the Farmworker Association of Florida. In a study that the association conducted with Emory University researchers, Economos told me that they found that more than 50 percent of farmworkers start each day dehydrated, and that after long days in the sun, a tenth of them can reach body temperatures of more than 101 degrees, which is in the danger zone for heat stroke.

At that forum, with experts who were fluent in both climate and health, with perhaps more M.D.s on display than Ph.D.s, it was made clear that climate change and health care cannot be considered as separate domains. Rather, just as environmental stresses such as pollen and pollutants are key components of public-health initiatives, so the effects of a warming world must first be concerns for doctors and public-health officials working to create healthy communities. On the one hand, these are not necessarily conversations that physicians are primed for. On the other, people generally trust their doctors, and America’s public-health system has provided the muscle for some of the most ambitious breakthroughs in terms of quality of life in the country’s history. With the realization that climate change will have serious and perhaps devastating effects on human health over the next century also comes the realization that it can be addressed as a public-health problem, and combatted with the same kinds of interventions that have proven effective in fighting tobacco use and drunk driving.

According to Georges Benjamin, the executive director of the APHA, “One of the central challenges that we do have is trying to encourage people that climate change is here today and is impacting our health today.” While polls do indicate that most Americans believe the climate is changing, and that it is caused by anthropogenic actions, there’s still a disconnect between that knowledge and informing the public of the tangible risks to their and their children’s lives. Additionally, public-health models currently stress the importance of enduring racial and class health disparities, which Benjamin thinks will only be made doubly worse by the effects of climate change, which will also likely affect vulnerable populations first. How can policy makers make people care about health problems that may be disproportionately affecting people who don’t look like them—in a country where bigotry is rampant and encouraged at the highest levels?

These are the points of consideration as a scientific movement at the intersection of climate change and public health truly begins to take off. The major debates at that intersection are no longer about whether the climate is changing, but the roles people should play in addressing it, who will be harmed, and how. For Benjamin, the role for the medical community is clear: “The way I think about it is: Somebody was made sick yesterday from climate change, someone is being made sick today as we speak, and someone is going to be made sick from climate change tomorrow.”

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Vann R. Newkirk II is a staff writer at The Atlantic, where he covers politics and policy.